Methods for making nearly planar dielectric films in integrated circuits

ABSTRACT

In the fabrication of integrated circuits, one specific technique for making surfaces flat is chemical-mechanical planarization. However, this technique is quite time consuming and expensive, particularly as applied to the numerous intermetal dielectric layers—the insulative layers sandwiched between layers of metal wiring—in integrated circuits. Accordingly, the inventor devised several methods for making nearly planar intermetal dielectric layers without the use of chemical-mechanical planarization and methods of modifying metal layout patterns to facilitate formation of dielectric layers with more uniform thickness. These methods of modifying metal layouts and making dielectric layers can be used in sequence to yield nearly planar intermetal dielectric layers with more uniform thickness.

RELATED APPLICATIONS

This application is a Divisional of U.S. application Ser. No.10/926,471, filed Aug. 26, 2004, which is a Divisional of U.S.application Ser. No. 10/677,057, filed Sep. 30, 2003, which is aDivisional of U.S. application Ser. No. 09/801,265, filed Mar. 7, 2001,now U.S. Pat. No. 6,627,549, which claims priority to U.S. ProvisionalApplication 60/187,658, filed on Mar. 7, 2000, all of which areincorporated herein by reference.

TECHNICAL FIELD

The present invention concerns methods of making integrated circuits,particularly methods of making metal masks and dielectric, orinsulative, films.

BACKGROUND OF THE INVENTION

Integrated circuits, the key components in thousands of electronic andcomputer products, are interconnected networks of electrical componentsfabricated on a common foundation, or substrate. Fabricators typicallybuild the circuits layer by layer, using techniques, such as doping,masking, and etching, to form thousands and even millions of microscopicresistors, transistors, and other electrical components on a siliconsubstrate, known as a wafer. The components are then wired, orinterconnected, together to define a specific electric circuit, such asa computer memory.

One important concern during fabrication is flatness, or planarity, ofvarious layers of the integrated circuit. For example, planaritysignificantly affects the accuracy of a photo-imaging process, known asphotomasking or photolithography, which entails focusing light onlight-sensitive materials to define specific patterns or structures in alayer of an integrated circuit. In this process, the presence of hillsand valleys in a layer forces various regions of the layer out of focus,causing photo-imaged features to be smaller or larger than intended.Moreover, hills and valleys can reflect light undesirably onto otherregions of a layer and add undesirable features, such as notches, todesired features. These problems can be largely avoided if the layer issufficiently planar.

One process for making surfaces flat or planar is known aschemical-mechanical planarization or polishing. Chemical-mechanicalplanarization typically entails applying a fluid containing abrasiveparticles to a surface of an integrated circuit, and polishing thesurface with a rotating polishing head. The process is used frequentlyto planarize the insulative, or dielectric, layers that lie betweenlayers of metal wiring in integrated circuits. These insulative layers,which typically consist of silicon dioxide, are sometimes calledintermetal dielectric layers. In conventional integrated-circuitfabrication, planarization of these layers is necessary because eachinsulative layer tends to follow the hills and valleys of the underlyingmetal wiring, similar to the way a bed sheet follows the contours ofwhatever it covers. Thus, fabricators generally deposit an insulativelayer much thicker than necessary to cover the metal wiring and thenplanarize the insulative layer to remove the hills and valleys.

Unfortunately, conventional methods of forming these intermetaldielectric layers suffer from at least two problems. First, the processof chemical-mechanical planarization is not only relatively costly butalso quite time consuming. And second, the thickness of these layersgenerally varies considerably from point to point because of underlyingwiring. Occasionally, the thickness variation leaves metal wiring undera layer too close to metal wiring on the layer, encouraging shorting orcrosstalking. Crosstalk, a phenomenon that also occurs in telephonesystems, occurs when signals from one wire are undesirable transferredor communicated to another nearby wire.

Accordingly, the art needs fabrication methods that reduce the need toplanarize internetal dielectric layers, that reduce thickness variationin these layers, and that improve their electrical properties generally.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a partial integrated-circuitassembly 10 including a substrate 12 and metal wires 14 a, 14 b, and 14c;

FIG. 2 is a cross-sectional view of the FIG. 1 integrated-circuitassembly after formation of a substantially planar insulative layer 16,including a portion 16 a with voids and a portion 16 b without voids;

FIG. 3 is a cross-sectional view of the FIG. 2 assembly after a facetetch to improve the planarity of layer 16;

FIG. 4 is a cross-sectional view of the FIG. 3 assembly after formationof metal wires 18 a and 18 b, and substantially planar insulative layer20, including a portion 20 a with voids and a portion 20 b withoutvoids;

FIG. 5 is a cross-sectional view of a partial integrated-circuitassembly 21 including a substrate 22 and metal wires 24 a, 24 b, and 24c;

FIG. 6 is a cross-sectional view of the FIG. 5 assembly after formationof an oxide spacer 26 and a substantially planar insulative layer 28,including a portion 28 a with voids and a portion 28 b without voids;

FIG. 7 is a cross-sectional view of the FIG. 6 assembly after a facetetch to improve the planarity of layer 28;

FIG. 8 is a cross-sectional view of the FIG. 7 assembly after formationof metal wires 30 a and 30 b, and substantially planar insulative layer34, including a portion 34 a with voids and a portion 34 b withoutvoids;

FIG. 9 is a cross-sectional view of a partial integrated-circuitassembly 35 including a substrate 36 and metal wires 36 a, 36 b, and 36c;

FIG. 10 is a cross-sectional view of the FIG. 9 assembly after formationof an oxide spacer 40 and a substantially planar insulative layer 42;

FIG. 11 is a flow chart illustrating an exemplary method of modifying ametal layout to facilitate fabrication of intermetal dielectric layerswith more uniform thickness;

FIG. 12 is a partial top view of a metal layout showing how theexemplary method of FIG. 11 adds metal to open areas in a metal layout;

FIG. 13 is a partial top view of a metal layout showing how theexemplary method of FIG. 11 fills notches in a metal layout;

FIG. 14 is a partial top view of a metal layout showing how theexemplary method of FIG. 11 fills corners in a metal layout;

FIG. 15 is a partial view of a metal layout showing how the exemplarymethod of FIG. 11 fills in between opposing edges of live metal regionsin a metal layout;

FIG. 16 is a partial view of a metal layout showing how the exemplarymethod of FIG. 11 moves edges;

FIG. 17 is a block diagram of an exemplary computer system 42 forhosting and executing a software implementation of the exemplarypattern-filling method of FIG. 11; and

FIG. 18 is a simplified schematic diagram of an exemplary integratedmemory circuit 50 that incorporates one or more nearly planar intermetaldielectric layers and/ or metal layers made in accord with exemplarymethods of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following detailed description, which references and incorporatesthe above-identified Figures, describes and illustrates specificembodiments of the invention. These embodiments, offered not to limitbut only to exemplify and teach the invention, are shown and describedin sufficient detail to enable those skilled in the art to implement orpractice the invention. Thus, where appropriate to avoid obscuring theinvention, the description may omit certain information known to thoseof skill in the art.

First Exemplary Method of Forming Nearly Planar Dielectric Films

FIGS. 1-4 show a number of exemplary integrated-circuit assemblies,which taken collectively and sequentially, illustrate an exemplarymethod of making nearly planar or quasi planar dielectric films, orlayers, within the scope of the present invention. As used herein, aquasi planar film is globally planar with local nonplanarities havingslopes less than or equal to 45 degrees and depths less than thethickness of the next metal layer to be deposited. The localnonplanarities typically occur over the gaps between underlying metalfeatures.

The method, as shown in FIG. 1, a cross-sectional view, begins withformation of an integrated-circuit assembly or structure 10, which canexist within any integrated circuit, for example, an integrated memorycircuit. Assembly 10 includes a substrate 12. The term “substrate,” asused herein, encompasses a semiconductor wafer as well as structureshaving one or more insulative, semi-insulative, conductive, orsemiconductive layers and materials. Thus, for example, the termembraces silicon-on-insulator, silicon-on-sapphire, and other advancedstructures.

Substrate 12 includes three representative wires or conductivestructures 14 a, 14 b, and 14 c, with a maximum (or average) featurespacing 14 s. In the exemplary embodiment, wires 14 a-14 c areapproximately 3000-6000 angstroms thick and comprise metals, such asaluminum, gold, or silver, and nonmetals, such as heavily dopedpolysilicon. Spacing 14 s, in the exemplary embodiment, is 0.3 microns.

Wires 14 a-14 c can be formed using any number of methods, for example,photolithography and dry etching. To avoid increasing feature spacingduring dry etching, the exemplary embodiment forms alateral-etch-resistant layer, that is, a layer resistant to lateraletching, on a metal layer before etching. Examples of suitable layersinclude a TEOS, oxide-nitride layer. Alternatively, one can addextensive serif features to the metal mask layout to avoid large openareas, especially to reduce the diagonal distance between features.

FIG. 2 shows that the exemplary method next entails forming aninsulative layer 16 over substrate 12 and wires 14 a-14 b. Layer 16 hasa thickness 16 t of, for example, 6000 angstroms, and includes twolayers or sublayers 16 a and 16 b. Sublayer 16 a includes a number ofvoids, particularly voids 17 between wires 14 a and 14 b, and betweenwires 14 b and 14 c, to increase its dielectric constant. Sublayer 16 bis either substantially voidless or includes a substantially fewernumber of voids than sublayer 16 a. The presence of voids in sublayer 16a reduces lateral electrical coupling between adjacent metal features,for example, between wires 14 a and 14 b and between wires 14 a-14 c andany overlying conductive structures.

The exemplary method forms layer 16 using a combination of anon-conformal and conformal oxide depositions. In particular, it uses aCVD TEOS (chemical vapor deposition tetraethyl-orthosilicate) or PECVDTEOS (plasma-enhanced CVD TEOS) oxide deposition process at anon-conformal deposition rate to form void-filled sublayer 16 a voidsand then lowers the TEOS deposition rate to, a conformal rate to formsubstantially voidless sublayer 16 b.

FIG. 3 shows that after forming sublayer 16 b, which includes some levelof nonplanarity, the exemplary method facet etches the sublayer at anangle of about 45 degrees to improve its global planarity. (That layer16 b has undergone further processing is highlighted by its newreference numeral 16 b′.) The facet etch reduces or smooths any sharptrenches in regions overlying gaps between metal features, such as wires14 a-14 c. As used herein, the term “facet etch” refers to any etchprocess that etches substantially faster in the horizontal directionthan in the vertical direction. Thus, for example, the term includes anangled sputter etch or reactive-ion etch.

To optimize the slopes of any vias, one can perform the facet etchbefore via printing. More specifically, one can facet etch after etchingany necessary vias and stripping photoresist to produce vias havinggreater slope and smoothness.

FIG. 4 shows the results of forming a second metallization levelaccording to the procedure outlined in FIGS. 1-3. In brief, this entailsforming conductive structures 18 a and 18 b on insulative sublayer 16 b′and forming an insulative layer 20 on sublayer 16 b′ and conductivestructures 18 a and 18 b. Insulative layer 20, like insulative layer 16,includes void-filled sublayer 20 a and substantially void-free sublayer20 b′. Sublayer 20 a includes one or more voids 19 between conductivestructures 18 a and 18 b. Sublayer 20 b′ was facet etch to improve itsplanarity. Layer 20 has a thickness 20 t, of for example 3000-6000angstroms.

Second Exemplary Method of Forming Nearly Planar Dielectric Films

FIGS. 5-8 show a number of exemplary integrated-circuit assemblies,which taken collectively and sequentially, illustrate a second exemplarymethod of making nearly planar or quasi planar dielectric layers withinthe scope of the present invention. The second method is particularlyapplicable to maximum metal feature spacing greater than about 0.3microns or oxide thickness less than 6000 angstroms to allow for shallowvia formation, that is, via depths less than about 4000 angstroms.

More particularly, FIG. 5 shows that the method begins with formation ofan integrated-circuit assembly or structure 21, which, like assembly 10in FIG. 1, can exist within any integrated circuit. Assembly 10 includesa substrate 22 which supports three representative wires or conductivestructures 24 a, 24 b, and 24 c, with a desired feature spacing 24 s. Inthe exemplary embodiment, spacing 24 s is greater than 0.3 microns. Someembodiments set a minimum spacing of 0.17 microns. However, the presentinvention is not limited to any particular spacing.

FIG. 6 shows that the exemplary method next entails forming aninsulative spacer 26 and an insulative layer 28. Insulative spacers 26,which consists of silicon dioxide for example, lies over portions ofsubstrate 22 adjacent wires 24 a-24 c to reduce the effective separationof wires 24 a-24 c. The exemplary method uses a TEOS oxide depositionand subsequent etching to form spacers 26. Insulative layer 28 has athickness 28 t of, for example, 4000 angstroms, and includes twosublayers 28 a and 28 b, analogous to sublayers 16 a and 16 b in thefirst embodiment. Specifically, sublayer 28 a includes a number of voids27 between the wires to increase its dielectric constant, and sublayer28 b is either substantially voidless or includes a substantially fewernumber of voids than sublayer 28 a. A two-stage TEOS oxide depositionprocess, similar to that used in the first embodiment, is used to formlayer 28.

FIG. 7 shows that after forming sublayer 28 b, which includes some levelof nonplanarity, the exemplary method facet etches the sublayer at anangle of about 45 degrees to improve its global planarity.

FIG. 8 shows the results of forming a second metallization levelaccording to the procedure outlined in FIGS. 5-7. This entails formingconductive structures 30 a and 30 b on insulative sublayer 28 b′ andforming an insulative spacer 32 and an insulative layer 34, which, likeinsulative layer 28, includes void-filled sublayer 34 a andsubstantially void-free sublayer 34 b′. Sublayer 34 a includes voids 31between conductive structures 30 a and 30 b, and sublayer 34 b′ is facetetched to improve its planarity.

Third Exemplary Method of Forming Nearly Planar Dielectric Films

FIGS. 9 and 10 show a number of exemplary integrated-circuit assemblies,which taken collectively and sequentially, illustrate a third exemplarymethod of making nearly planar or quasi planar dielectric layers withinthe scope of the present invention. In contrast to the first and secondembodiment, the third exemplary embodiment is intended for forminginsulative films on metal layers with maximum feature spacing up toabout 0.5 microns.

FIG. 9 shows that the method begins with formation of anintegrated-circuit assembly or structure 35, which like assembly 10 inFIG. 1 and assembly 21 in FIG. 5, can exist within any integratedcircuit. Assembly 35 includes a substrate 36 which supports threerepresentative wires or conductive structures 38 a, 38 b, and 38 c, witha desired feature spacing 38 s of about 0.5 microns.

FIG. 10 shows the results of forming an oxide spacers 40 and aninsulative layer 42. The exemplary embodiment forms one or more oxidespacers 40 which is about 1000 angstroms wide, and thus reduces theeffective spacing between conductors 38 a-38 c by 2000 angstroms.Forming insulative layer 42 entails executing a flow-fill procedure,such as TRIKON-200 by Trikon Technologies, Inc. To obtain global andlocal planarity, one can reduce the maximum feature space by usingoxide/TEOS spacer as taught in the second exemplary method, or byenlarging the metal feature, or by adding floating metal between themetal features.

Exemplary Method of Promoting Uniform Thickness of Intermetal DielectricLayers

To facilitate the formation of more uniformly thick inter-metaldielectric layers, such as those described above, the inventor developedspecific methods of (and related computer software) for increasing thepattern density of metal layouts. The methods and associated softwaretake a given metal layout and modify, or fill, open areas of the layoutto increase pattern density and thus promote uniform thickness or reducethickness variation across dielectric layers formed on metal layersbased on the layouts. These methods and software can thus be used, forexample, to facilitate formation of the conductive structures shown inFIGS. 1, 5, and 9.

The exemplary method generally entails iteratively measuring a givenlayout, adding floating metal to fill large open areas in the layout,and extending or filling out existing metal areas to meet maximumfeature spacing, or gap, criteria. FIG. 11 shows a flow chart of theexemplary method, which is suitable for implementation as acomputer-executable program.

Specifically, the flow chart includes a number of process or decisionblocks 110, 120, 130, and 140. The exemplary method begins at processblock 110 which entails measuring a given layout. This entailsdetermining open (unmetallized or nonconductive) areas large enough tobe filled with floating metal and identifying live metal areas thatrequire additional metal to obtain desired spacing. Floating metal ismetal that is not coupled to a signal path or component, whereas livemetal is metal that is coupled to a signal path or component.

After executing block 110, the exemplary method proceeds to block 120which entails adding floating metal to any large areas identified inblock 110. To illustrate, FIG. 12 shows a hypothetical layout having alive metal region 200 with open area 210. In general, if dimension A isgreater than the sum of dimension S1, dimension S2, and L (the maximumfeature spacing criteria), the exemplary method adds floating metal,such as floating metal region 220.

After adding floating metal, the exemplary method adds live metal asindicated in block 120 of FIG. 11. FIG. 12 is again instructive of theexemplary method. If dimension B is less than the sum of dimension SI,dimension S2, and L, the exemplary method adds metal as indicated byadded active metal region 230 process block 104 which entails filling innotches in the layout.

More particularly, the exemplary method follows an iterative process foradding live (or non-floating) metal, as indicated by blocks 130 a-130 g.

Block 130 a entails filling notches in the current live metal. FIG. 13shows a live metal region 300 of a hypothetical metal layout having anotch 310. Included within notch 310 are a series of iteratively addedlive metal regions 320-325. The amount of metal added at each iterationcan be selected using a minimum surface area criteria or computeddynamically each iteration. The exemplary embodiment repeatedly addsmetal to the notch until it is filled, before advancing to block 310 b.However, other embodiments can advance to block 310 b before the notchis filled, relying on subsequent trips or iterations through the firstloop in the flowchart to complete filling of the notch.

Block 130 b entails filling in corners in the current live metal,meaning the live metal after filling notches. FIG. 14 illustrates a livemetal region 400 having a corner 410 and added L-shaped live metalregions 420-423 and a rectangular live metal region 424. (Otherembodiments add other shapes of live metal regions.) The amount of metaladded at each iteration can be selected using a minimum surface area orsingle-dimensional criteria or computed dynamically each iteration. Theexemplary embodiment repeatedly adds metal to the corner until it isfilled, before advancing to block 130 c. However, other embodiments canadvance to block 310 b before the notch is filled, relying on subsequenttrips through the inner loop to complete filling of the notch.

Block 130 c entails filling in between opposing edges of adjacent livemetal regions to achieve a desired spacing, such as a maximum desiredspacing L. FIG. 15 shows live metal regions 510 and 520, which haverespective opposing edges 510 a and 520 a. The exemplary method entailsadding live metal regions, such as live metal regions 521-523, one edgesuch as edge 520 a to achieved the maximum desired spacing L. However,other embodiments add live metal to both of the opposing edges toachieve the desired spacing. Still other embodiments look at the lengthsof the opposing edges and use one or both of the lengths to determineone or more dimensions of the added live metal regions.

After filling in between opposing edges of existing live metal regions,the exemplary method advances to decision block 130 d in FIG. 11. Thisblock entails determining whether more live metal can be added. Moreprecisely, this entails measuring the layout as modified by the livemetal already added and determining whether there are any adjacentregions that violate the desired maximum spacing criteria. (Note thatsome exemplary embodiments include more than one maximum spacingcriteria to account for areas where capacitive effects or crosstalkissues are of greater importance than others.) If the determinationindicates that more metal can be added execution proceeds back to block130 a to fill in remaining notches, and so forth. If the determinationindicates that no more live metal can be added to satisfy the maximumspacing criteria, execution to proceeds to block 130 e in FIG. 11.

Block 130 e entails moving (or redefining) one or more edges (orportions of edges) of live metal regions in the modified layoutspecification. To illustrate, FIG. 16 shows live metal regions 610 and620, which have respective edges 610 a and 620 a. It also shows theaddition of live metal region 630 to edge 620 a, which effectivelyextends the edge. Similarly, edge 620 a has been extended with theiterative addition of live metal regions 631 and 632. The additions canbe made iteratively using a dynamic or static step size, or all it onceby computing the size of an optimal addition to each edge. Exemplaryexecution then proceeds to decision block 130 f.

In decision block 130 f, the exemplary method decides again whether moremetal can be added to the layout. If more metal can be added, theexemplary method repeats execution of process blocks 104-122. However,if no metal can be added, the method proceeds to process block 140 tooutput the modified layout for use in a fabrication process.

Although not show explicitly in the exemplary flow chart in FIG. 11, theexemplary method performs data compaction to minimize or reduce theamount of layout data carried forward from iteration to iteration. Datacompaction reduces the number of cells which define the circuitassociated with the metal layout and the computing power necessary tocreate the metal layout.

The exemplary compaction scheme flattens all array placement into singleinstance placements. For example, a single array placement of a cellincorporating a 3×4 matrix flattens to 12 instances of a single cell. Italso flattens specific cells, such as array core cells, vias, orcontacts, based on layout or user settings. Additionally, it flattenscells which contain less than a predetermined number of shapesregardless of any other effects. For example, one can flatten cellshaving less than 10, 20, or 40 shapes. Lastly, the exemplary compactionscheme attempts to merge shapes to minimize overlapping shapes andredundant data.

The appropriate or optimum degree of flattening depends largely on theprocessing power and memory capabilities of the computer executing theexemplary method. Faster computers with more core memory and swap spacecan handle larger number of shapes per cell and thus have less need forflattening than slower computers with less core memory and swap space.In the extreme, a complete circuit layout can be flattened into onecell.

If a given layout design is not a single flat list of shapes butincludes two or more cells placed into each other as instances,additional precaution should be taken to reduce the risk of introducingunintended shorts into the layout during the pattern-fill process. Inthe exemplary embodiment, this entails managing the hierarchy of cells.

The exemplary embodiment implements a hierarchy management process whichrecognizes that each cell has an associated fill area that will notchange throughout the metal-fill process. The exemplary managementprocess entails executing the following steps from the bottom up untilall cell dependencies are resolved. For each instance in each cell, theprocess creates a temporary unique copy of the cell associated with agiven instance. After this, the process copies metal from other cellsinto the cell being examined if it falls into the fill area. The processthen copies metal from other cell into the cell if the metal falls intoa ring around the fill area. Next, the process identifies, extracts, andmarks conflict areas.

This exemplary pattern-filling method and other simpler or more complexmethods embodying one or more filling techniques of the exemplaryembodiment can be used in combination with the methods of making nearlyplanar intermetal dielectric layers described using FIGS. 1-10. Moreprecisely, one can use a pattern-filling method according to theinvention to define a layout for a particular metal layer, form a metallayer based on the layout, and then form a nearly planar intermetaldielectric layer according to the invention on the metal layer. Thecombination of these methods promises to yield not only a nearly planardielectric layer that reduces or avoids the need for chemical-mechanicalplanarization, but also a dielectric layer with less thickness deviationbecause of the adjusted pattern fill density of the underlying metallayer.

Exemplary Computer System Incorporating Pattern-Filling Method

FIG. 17 shows an exemplary computer system or workstation 42 for hostingand executing a software implementation of the exemplary pattern-fillingmethod. The most pertinent features of system 42 include a processor 44,a local memory 45 and a data-storage device 46. Additionally, system 42includes display devices 47 and user-interface devices 48. Someembodiments use distributed processors or parallel processors, and otherembodiments use one or more of the following data-storage devices: aread-only memory (ROM), a random-access-memory (RAM), anelectrically-erasable and programmable-read-only memory (EEPROM), anoptical disk, or a floppy disk. Exemplary display devices include acolor monitor, and exemplary user-interface devices include a keyboard,mouse, joystick, or microphone. Thus, the invention is not limited toany genus or species of computerized platforms.

Data-storage device 46 includes layout-development software 46 a,pattern-filling software 46 b, an exemplary input metal layout 46 c, andan exemplary output metal layout 46 d. (Software 46 a and 46 b can beinstalled on system 42 separately or in combination through anetwork-download or through a computer-readable medium, such as anoptical or magnetic disc, or through other software transfer methods.)Exemplary storage devices include hard disk drives, optical disk drives,or floppy disk drives. In the exemplary embodiment, software 46 b is anadd-on tool to layout-development software 46 a and layout 46 c wasdeveloped using software 46 a. However, in other embodiments, software46 b operates as a separate application program and layout 46 c wasdeveloped by non-resident layout-development software. General examplesof suitable layout-development software are available from Cadence andMentor Graphics. Thus, the invention is not limited to any particulargenus or species of layout-development software.

Exemplary Integrated Memory Circuit

FIG. 18 shows an exemplary integrated memory circuit 50 thatincorporates one or more nearly planar intermetal dielectric layersand/or metal layers within the scope of the present invention. One morememory circuits resembling circuit 50 can be used in a variety ofcomputer or computerized systems, such as system 42 of FIG. 17.

Memory circuit 50, which operates according to well-known and understoodprinciples, is generally coupled to a processor (not shown) to form acomputer system. More particularly, circuit 50 includes a memory array52, which comprises a number of memory cells 53 a, 53 b, 53 c, and 53 d;a column address decoder 54, and a row address decoder 55; bit lines 56a and 56 b; word lines 57 a and 57 b; and voltage-sense-amplifiercircuit 58 coupled in conventional fashion to bit lines 56 a and 56 b.(For clarity, FIG. 18 omits many conventional elements of a memorycircuit.)

Conclusion

In furtherance of the art, the inventor has presented several methodsfor making nearly planar intermetal dielectric layers without the use ofchemical-mechanical planarization. Additionally, the inventor haspresented a method of modifying metal layouts to facilitate formation ofdielectric films with more uniform thickness. These methods of modifyingmetal layouts and making dielectric layers can be used in sequence toyield nearly planar intermetal dielectric layers with more uniformthickness.

Various methods are disclosed of making dielectric layers on metallayers, which reduce the need for chemical-mechanical planarizationprocedure. Specifically, a first exemplary method of the invention formsa metal layer with a predetermined maximum feature spacing and then usesa TEOS-based (tetraethyl-orthosilicate-based) oxide deposition procedureto form an oxide film having nearly planar or quasi-planarcharacteristics. The exemplary method executes a CVD (chemical vapordeposition) TEOS oxide procedure to form an oxide layer on a metal layerhaving a maximum feature spacing of 0.2-0.5 microns.

A second exemplary method includes voids within the oxide, or moregenerally insulative, film to improve its effective dielectric constantand thus improve its ability to prevent shorting and crosstalk betweenmetal wiring. Specifically, the exemplary method uses a TEOS process ata non-conformal rate sufficient to encourage the formation of voids, andthen uses the TEOS process at a conformal rate of deposition to seal thevoids. More generally, however, the invention uses a non-conformaldeposition procedure to encourage formation of voids and then a moreconformal deposition to seal the voids.

A third exemplary method increases the metal-fill density of metalpatterns to facilitate formation of intermetal dielectric layers havingmore uniform thicknesses. The third exemplary method adds floating metalto open areas in a metal layout and then extends non-floating metaldimensions according to an iterative procedure that entails filling innotches, and corners and moving selected edges of the layout.

The embodiments described above are intended only to illustrate andteach one or more ways of practicing or implementing the presentinvention, not to restrict its breadth or scope. The actual scope of theinvention, which embraces all ways of practicing or implementing theinvention, is defined only by the following claims and theirequivalents.

1. An integrated circuit, comprising: one or more conductors; a firstinsulative layer which is substantially free of voids and which contactsthe one or more conductors; a second insulative layer which lies of thefirst insulative layer and which includes a substantial number of voids.2. The integrated circuit of claim 1, wherein the first and secondinsulative layers consist essentially of silicon oxide and havesubstantially different dielectric constants.
 3. An integrated circuit,comprising: one or more memory cells; one or more conductors coupled tothe one or more memory cells; a first insulative layer which issubstantially free of voids and which contacts the one or moreconductors; and a second insulative layer which lies on the firstinsulative layer and which includes a substantial number of voids. 4.The integrated circuit of claim 3, wherein the first and secondinsulative layers consist essentially of silicon oxide and havesubstantially different dielectric constants.
 5. A system, comprising:at least one integrated circuit, including a processor; at least oneintegrated memory circuit operable coupled to the processor, comprising;one or more memory cells; one or more conductors coupled to the one ormore memory cells; a first insulative layer which is substantially freeof voids and which contacts the one or more conductors; a secondinsulative layer which lies on the first insulative layer and whichincludes a substantial number of voids.
 6. The system of claim 5,wherein the first and second insulative layers consist essentially ofsilicon oxide and have substantially different dielectric constants. 7.The system of claim 5, wherein the processor is a digital signalprocessor.
 8. An integrated circuit, comprising: one or more conductorsincluding an oxide spacer on one or more lateral sides of each of theconductors; a first insulative layer having a first thickness disposedupon the one or more conductors and formed at a first deposition rate toform voids in the first insulative layer; and a second insulative layerhaving a second thickness disposed upon the first insulative layer andformed at a second deposition rate to form a substantially void freelayer.
 9. The integrated circuit of claim 8, wherein the first andsecond insulative layers consist of silicon oxide and have differentdielectric constants.
 10. The integrated circuit of claim 8, wherein thesecond deposition rate is less than the first deposition rate.
 11. Theintegrated circuit of claim 8, wherein the second insulative layer isfacet etched to form sloping sides.
 12. The integrated circuit of claim8, wherein the insulative layers include at least one via hole formed inthe first and second insulative layers, and at least the secondinsulative layer is at least one of facet etched and thermally reflowedto form sloping sides of the at least one via hole.
 13. The integratedcircuit of claim 8, wherein the one or more conductors further include afilm resistant to lateral etching deposited upon the conductors.
 14. Theintegrated circuit of claim 13, wherein the film resistant to lateraletching is a TEOS, oxide-nitride film.
 15. An integrated circuit,comprising: a first insulative layer having a first thickness and afirst dielectric constant disposed upon one or more conductors andformed at a first deposition rate to form voids in the first insulativelayer; a second insulative layer having a second thickness and a seconddielectric constant disposed upon the first insulative layer and formedat a second deposition rate that is less than the first deposition rateto form a substantially void free layer; and the first and secondinsulative layers include at least one via hole formed in the first andsecond insulative layers, and at least the second insulative layer is atleast one of facet etched and thermally reflowed to form sloping sidesof the at least one via hole.
 16. The integrated circuit of claim 15,wherein the first and second insulative layers include at least one ofsilicon dioxide, silicon oxide, silicon rich oxide, a silicon oxynitrideand a silicon nitride; and wherein the one or more conductors include adielectric spacer on one or more lateral sides of each of the conductorsfilm that is resistant to lateral etching and formed of at least one ofan oxide, an oxynitride, a nitride, a TEOS oxide, a TEOS oxynitride, aTEOS nitride, a spin-on dielectric, and a plasma oxide.
 17. Anintegrated circuit, comprising: a plurality of conductors; a firstinsulative layer having a first thickness disposed upon the plurality ofconductors and formed at a first deposition rate to form voids in thefirst insulative layer; a second insulative layer having a secondthickness disposed upon the first insulative layer and formed at asecond deposition rate to form a substantially void free layer; whereinthe plurality of conductors are disposed relative to one another to havea minimum separation and a maximum separation provided by individualones of the plurality of conductors having a separation greater than themaximum separation, have at least one of a plurality of metal featuresinserted between the individual conductors, the feature selected fromthe list of pieces of metal including, a floating piece, a notch fillingpiece, a corner filling piece, and a between edges filling piece. 18.The integrated circuit of claim 17, wherein the plurality of metalfeatures have a width determined by a difference between the separationgreater than the maximum separation of the individual ones of theplurality of conductors disposed relative to one another, and theminimum separation value to provide a separation approximately equal tothe minimum separation.
 19. The integrated circuit of claim 18, whereinthe plurality of metal features are selected by providing a first metallayout pattern having a first fill density; generating a second metallayout pattern based upon the first metal layout pattern by identifyingindividual ones of the plurality of conductors having a separationgreater than the maximum separation; filling in one or more open areasof the first metal layout pattern having a separation greater than apredetermined value with floating metal; filling in one or more notchesin the first metal layout pattern having less than the predeterminedvalue and more than the maximum value with added metal to at least oneof the plurality of conductors; filling in one or more corners of thefirst metal layout having less than the predetermined value and morethan the maximum value with added metal to at least one of the pluralityof conductors; filling in one or more opposing edges of the first metallayout having less than the predetermined value and more than themaximum value with added metal to at least one of the plurality ofconductors; generating a second fill density for the second metal layoutpattern and repeating the identifying the individual ones of theplurality of conductors having a separation greater than the maximumseparation; and continuing to generate metal layout patterns until atleast one of a predetermined number of iterations occurs, and until noneof the individual ones of the plurality of conductors has more than themaximum separation.
 20. An integrated circuit, comprising: a pluralityof conductors including an oxide spacer on one or more lateral sides ofat least one of the conductors; a first insulative layer having a firstthickness disposed upon the plurality of conductors and formed at afirst deposition rate to form voids in the first insulative layer; asecond insulative layer having a second thickness disposed upon thefirst insulative layer and formed at a second deposition rate to form asubstantially void free layer; wherein the plurality of conductors aredisposed relative to one another to have a minimum separation and amaximum separation; wherein the separation is determined by providing afirst metal layout pattern having a first fill density; generating asecond metal layout pattern based upon the first metal layout pattern byidentifying individual ones of the plurality of conductors having aseparation greater than the maximum separation; filling in one or moreopen areas of the first metal layout pattern having a separation greaterthan a predetermined value with floating metal; filling in one or morenotches in the first metal layout pattern having less than thepredetermined value and more than the maximum value with added metal toat least one of the plurality of conductors; filling in one or morecorners of the first metal layout having less than the predeterminedvalue and more than the maximum value with added metal to at least oneof the plurality of conductors; filling in one or more opposing edges ofthe first metal layout having less than the predetermined value and morethan the maximum value with added metal to at least one of the pluralityof conductors; generating a second fill density for the second metallayout pattern and repeating the identifying the individual ones of theplurality of conductors having a separation greater than the maximumseparation; and continuing to generate metal layout patterns until atleast one of a predetermined number of iterations occurs, and until noneof the individual ones of the plurality of conductors has more than themaximum separation.
 21. The integrated circuit of claim 20, wherein thefirst and second insulative layers consist essentially of silicon oxideand have substantially different dielectric constants, and the seconddeposition rate is less than the first deposition rate.
 22. Theintegrated circuit of claim 20, wherein the insulative layers include atleast one via hole formed in the first and second insulative layers, andat least the second insulative layer is at least one of facet etched andthermally reflowed to form sloping sides of the at least one via hole.